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Patented 19, 1929.

outrun srarus PATENT OFFICE.

LINN BRADLEY, OF MONTCLAIB, NEV] JEBSEY, AND EDWARD l. MCKEEFE, 0F PLATTS- BURG-I-I, NEW YORK, ASSIGNORS TO BRADLEY-MGKEEFE CORPORATION, OF NEW YORK, N. Y., A. CORPORATION OF NIH/V YORK.

PRODUCTION OF COMPOSITE COOKING LIQUOR.

No Drawing. Original application filed February 8, 1932-2, Serial No. 535,034.

filed March 2, 1925.

This invention relates to improvements in the production of composite cooking liquors containing caustic soda and a three element sodium compound containing sulfur, such as sodium sullite, either with or without other sodium compounds. More particularly, the invention relates to an improved process o't treating the residual liquors resulting from the cooking of wood with a composite liquor containing caustic soda and sodium sull'ite for the regeneration of cooking liquors therefrom for use in the further carrying out of the cooking process.

In our prior parent appli ation, Serial No. 535.03%, liled February 8, 1922, we have described a process for the production of wood pulp from wood which is carried out with a cooking liquor consisting essentially of caustic soda together with normal sodium suilitc, with the caustic soda present in preponderating amount, that is, with the amount oi so dium present sultite not exceed ng the amount of sodium present as caustic soda, and ordinarily with the amount of sodium suliite smallerin sodium content than that of the caustic soda, for example, from ten to twenty-live percent of the total sodium present being present as sodium sullite. In such cooking processes, the caustic soda although in preponderating amount, is nevertheless so controlled in amount and concentration in the cooking liquor that it does not exert any excessively destructive action on the ii ors oi the wood.

The residual liquors produced as result of such cooking process are themselves of distinctive composition and can be readily treated, according to the present invention, for the regeneration of the cooking liquors. lVe have found that these residual liquors can be advantageously treated by the ordinary procedure and apparatus employed in the treatment of black liquors from the soda process, provided the operations are specially regulated, and even though the residual liquors and cooking liquors oi the present invention contains considerable amount of sodium sulfite.

The composition of the cooking liquor used in the cooking process, and which is to be regenerated by the process of the present invention, may vary somewhat in its composition.

Divided and this application Serial No. 12,762.

The cooking liquor may, for example, for poplar wood, have a strength of about 1f 0 or 16 'liwaddell and may be e. g. of 90% caustici'ty based on Na CO In general, the liquors may contain from 50 to grams per liter of causticsoda and from l0 to 25 grams per liter of normal sodium suliite, although an even larger amount oi. sullite, up to an amount equal. to that of the caustic soda may he used, preferably with corresponding reduction in the amount and proportion of the caustic soda. lVith dense hard woods a radically increased amount oi the reagents should be used, but in that use the sodium suh'ite should be increased, without a corresponding increase in caustic soda, so that the amount and strength of caustic soda in the composite cooking liquor will be kept below the an'rount which will cause any considerable injury to the fibers of the pulp produced. For example, with dense hard woods, the cooking liquor may be made up of caustic soda and sodium sulfite in approximately equal amounts, so liar as their sodium content is concerned.

It is one advantage of the cooking process using such a composite cooking liquor that a materially increased yield of pulp is obtained from the wood, and a correspondingly decreased amount of the wood substance is dissolved away into the residual liquors, as compared, for example, with the soda process. The residual liquors, moreover, are distinguished in their properties and composition from the ordinary black liquor of the soda process, and also from the so-called black liquor ot' the sulfate process. The residual liquors are also distinguished from the socalled waste sultite liquors of the acid sullite process. The residual liquor, like the cookingliquor. is of a composite character. The cooking process combines the reactions of the caustic soda and of the sulfite present, although the liquor is not acid, as is the liquor of the acid sulfite process, nor is it as strongly alkaline as the liquor of the ordinary soda process.

If the residual liquors, made with the composite caustic and suliite cooking liquor, were concentrated and calcined under strongly OX- idizing conditions, the greater part or all of the sullite or sulfite-reaction products would be decomposed with setting free of sulfur dioXide and the formation of sodium carbonate as the primary if not the sole sodium compound of the calcined product. ()n the other hand, if the residual. liquor is cm'icentrated and subjected to calcination under smelting conditions, reduction of the sulfite or sulfi reaction products will take place to a greater or lesser extent, with the resulting productioi'i of sodium sulfide in the calcined product. The former process included in our former co-pending application Serial N o. 513,161, filed November the latter in our copending application Seria No. (586,137, filed January M, 1924.

According to the present invention, the residual liquor is concentrated and then calcined under regulated conditions, whereby a considerable amount of sodium sulfite is directly recovered, together with sodium carbonate, and ivith or Without small and. vary ing' amounts of other sodium salts, from the calcined product.

'We have found that the residual liquors can be readily treated for the regeneration of the cooking liquors by subjecting them to evaporation in multiple effect evaporators and by calcining the resulting concentrated liquor in rotary calcining furnaces, such as used in the calcining of black liquor from the ordinary soda process. Owing to the decreased ainunt of Wood substance contained in solution in the residual liquors (e. from poplar Wood), the liquors are less gummy in character and give less trouble in the evaporators from foaming or gumming, etc. The liquor, from the strong liquor tank, of a strength of around 14 0014.5 Tivaddell at a temperature of 155 to 160 F. can be readily concentrated in. quadrimle effect evaporators to 60 or 'llwaddell, or even higher, at a temperature of 140 to M4 F. The concentrated liquor can then be fed to the rotary calcining furnaces such as are used in treating black liquors from the ordinary soda process.

e have found that, although the residual liquors contain a considerable amount of combined sulfur they can nevertheless be calcined in the rotary furnaces Without driving oil the entire amount of the combined sulfur. \Vc have also found that sodium sulfite comes from the rotary calcining furnaces Without any considerable amount of reduction by the admixed organic matter, a few per cent, only of sulfide being formed. The rotary caleining furnaces may, for example, have a diameter of about 9 feet and a length of about 16 feet and may be heated by coal fire. The concentrated residual liquor from the mul tiple effect evaporators, concentrated to about 60-65 Twaddell can be fed into the rotary furnaces at one end and the calcined productdischarged at the other. With proper control of the calci'nation, such that fusion of the dischar ed product is avoided as much as possible, the sulfite comes from the furnace in considerable amount.

The calcined product can then be leached, example, by introducing it into Water and ating the water, or by otherwise carrying out the leaching operation. By countercurrent leaching a solution can be obtained up to 273 Twaddell. This liquor can be subjected to causticizing with lime to convert its contained sodium carbonate for the most part into caustic soda, using, for example, 53 or 5% parts of calcium oxide to 100 parts of sodium carbonate. The sulfile contained in the liquor is advantageously not causticized, and the amount of lime should be kept sufliciently low to avoid this. The causticizing operation can be carried out by heating and agi ating for a sufficient period of time to carry the causticizing to the desired degree. some sodium carbonate will usually be left uncausticized in the resulting liquor, which will be made up for the most part of caustic soda, resulting from the causticizing operation, and sodium suliite. Some small and incidental amount of sodium sulfide may also be present, produced during the calcination, but We have found that, by avoiding smeltingof the charge during calcination, there is no building up of sulfide to an objectionable degree nor is there any excessive building up of sulfate, but the sulfite in considerable part passes through the furnace and is recovered for further use, while such small and incidental amounts of sodium sulfide as may be formed and as may be present in the regenerated liquor, are Without any objectionable effect in the process when carried out with the regenerated cooking liquor, although such amounts of sodium sulfide can be readily removed, if desired.

In order to make up for losses of caustic soda and sodium sulfite, a suitable amount of dry soda ash, for example, may be added to the liquor before causticizing, While the necessary amount of sodium sulfite can be readily produced, for example, by burning sulfur in a small sulfur burner and absorbing the sulfur dioxide in a. solution of soda ash or a solution which contains the sodium carbonate le ched from the calcined product above dc- .ibed.

V The process of the present invention enables the pulp manufacture to be made regenerative or cyclic in character, with the use of a cooking liquor of a composite character, containing essentially caustic soda and sodium sulfite, and With treatment of the residual liquors for the regeneration therefrom of the cooking liquor containing essentially the same ingredients, with. or Without the admixture of small and varying amounts of other ingredients. This cyclic or re enerative process involves the cooking of the Wood chips with the composite cooking liquor,

evaporation of the residual liquor and calcination of the concentrated liquor, with regulation of the calcining operation, and with avoiding 0t smelting, so that. the sodium sulfite and other required chemicals are recovered'without excessive loss, and with leaching of the calcined material and causticizing ot the leached liquor 'ith lime, using a rogu lated amount of lime such that the maj or por tion of the sodium carbonate is causticizod without, however, ca-usticizing the sodium sullile, thus reco'v'ering essentially a mixture oil. caustic soda and sodium sultite in a form available for use in the further carrying out of the process, with such additions as may be required to make up the composition of the liquor to that desired in the cooking operation.

The residual liquor treated in the process ot the present invention, is, as above stated, oil a distinctive and cha-riu'teristic composition. It contains less dissolved fibrous material and consequently less organic matter. Itcau. be readily evaporated without di'llicult-v: and it acts in a characteristic way whensubjected to calcination. and when the *alcining operation regulated in the manner above described. From the calcined material the new cooking liquor can be produced by a regulated causticizing operation, regulated and controlled in the manner above indicated, with addition of fresh amounts of chemicals to make up tor losses of soda or of the sultite radical during the regenerative process.

The residual liquors treated in the present process, because of their diilercnt composition, and particularly because of their content of three element sodium salts containing sulfur, are readily used unless proper control of the calcination is ell'ected. With such proper control. fusion can be avoided to such an extent that the sullite comes from the turnace and is present in the calcined product in considerable amount. h'lorcover, by avoiding smelting ot the charge during calcinalion. and regulating the calcination to avoid smelting, there is no building up (it sullidc to an objectionable degree, but the sultite in considerable part pa. s through the Furnace and is recovered for further use. t uch small and incidental amounts of sodium sulfide as mav be Formed and as may be present in tho liqiior leached trom the calcined product may be loft: in the liquor or may he removed. When the leached liquor is used tor absorbing sulfur dioxide, some or all o t' the sullidc will be converted into thiosult'atc and the latter will then be present in the regenerated liquor.

The recovery of some of the desired three element sodium compounds containing sult'ur, such as sodium sultite, from the calcined product, reduces to a corresponding extent the amount of such compounds which it is necessary to add or form by further treatment from the leached liquor. Moreover, when the leached liquor, with its large con tent of sodium carbonate, is causticized, the causti *izing operation is regulated to convert the desired amount of sodium carbonate into caustic soda, but without causticizing the dcsircd thrcc clement smlium-sullfur compounds, such as sodium sullitc. The present invention, accordingly, includes a partial or "fractional causticizing of the leached liquor with. an amount oi lime iusutlicicnt to causticize the sodium sullite, etc. content.- of the liquor, but sutlicient to causticize the sodium carbonate content to the desired degree.

We do not claim herein the complete or :lic process for the manufacture of pulp and paper which includes the tr *atment oi? residual liquor in accordance with the present application, inasmuch as this complete cyclic process is claimed in our parent application Serial No. 535,03.

l'v'e claim l. The method of regenerating a cooking liquor containing caustic soda and sodium sultite from a residual liquor resulting .t'rom the cooking of wood with such a cooking liquor, which comprises concentrating the residual liquor, calcining the same in a 1'Ul1211' :turnacc under conditions to give a calcined product containing sodium sullite and sodium 'arbonatc, leaching the calcined material and c-austicizing the resultin solution with an amount of lime insuliici nt to causticize the sodium sultite therein. I

2. The method of treating residual liquor, resulting from the cooking of wood with a cooking liquor containing a preponderating amount Of caustic soda and a lesser amount of sodium sullite which comprises subjecting the liquor to concentration and calcination, regulating the 'alcination to avoid an considerable fusion of the calcined product, leaching the calcined product and incompletely causticizing the resulting solution.

3. The method of treating residual liquor resulting from the cooking of wood with a cooking liquor containing sodium sulfitc which comprises subjecting the liquor to concentratiou and calcinat-ion and regulating the calcining operation to avoid smelting ot the calcined product.

The method. of lrea iing residual liquor remitting from the cooking of wood with a cooking liquor crmtaining sodium sullitc which (KHUPl'lSQS subjecting the liquor to concenlration and calcination and regulating the calcining operation to give a calcined product containing a considerable amount ol" sodium sulfite.

The method o't treating residual liquor, resulting from the cooking 0t wood with a cooking liquor containing a preponderating amount of caustic soda and a lesser amount of sodium sulfite which comprises subjecting the iii liquor to concentration and calcination, and regulating the calcination to avoid any considerable fusion of the calcined product.

6. The method of treating residual liquor, resulting from the cooking of wood with a cooking liquor containing sodium suliite, which comprises subjecting the li nor concentration and calcination, and reg ilating the calciiultion to avoid any conshlerable fusion of the calcined product.

7. The method of treating residual liquor, resulting from the cooking ct wood with a cooking liquor containing cans soda and also containing a three element compound of sodium which contains sulfur, which coinprises subjecting the liquor to coi'icentration and calcination, and regulating the calcination to avoid any considerable fusion of the calcined product.

8. The method of treating residur resulting from the cooking of wooiii cooking liquor containing caustic soda and also containing a three element (01111 iound of sodium which contains sulfur, which coinprises subjecting the liquor to concenti" and calcination, regulating the calcinatiou to avoid smelting, leaching the calcined product and incompletely causticizing the resulting solution.

9. The method of treating residual liquor, resulting from the cooking of wood with a cooking liquor containing caustic soda and also containing a three element conqiound of sodium which contains sulfur, which coinprises concentrating the liquor, supp ng the concentrated liquor to a calcining furnace with completion of the evaporation and production of a calcined product, and regulating the calcining operation to avoid Sii'ltllik ing of the calcined product.

10. The method of treating residual liquor, resulting from the cooking of wood with a cooking liquor containing caustic soda and also containing a. three elementcompound of sodium which contains sulfur, which o prises concentrating the liquor in inn effect evaporators, supplying the concentrated liquor to a rotary calcining furnace with resulting conqiletion of ei'tqioratio and production of a calcined product an x, lating the calcining operation to avoiu i considerable fusion of the calcined pro uct.

11. A proccs of recovering sodium sulfur salts from residual liquor, resulting from the cooking of wood with a cooking liquor containing caustic soda and illilt element ,odiuni sulfur salts. which includes the step 01 supplying the liquor to acalciniug furnace and evaporating the liquor to dryness and calcining the dried product therein, the calcining being regulated to avoid smelting of the calcined product.

12. The method of treating residual liquor, resulting from the cooking of wood with a cooking liquor containing caustic soda and also containing a three element compound of sodium which contains sulfur, which coniconccntrating the liquor in multiple ehcct evaporators, supplying the concentrated liquor to a rotary calcining furnace with resultin completion of evaporation and production of a calcined product, regulating the calcining operation to avoid any considerable fusion of the calcined product, teaching the calcined product and lUCUHlPlClTQ- ly causticiiaing the leached liquor.

13. A process of recovering sodium sulfur salt from residual liquor, resulting from the cooking of wood with a cooking liquor containing caustic soda and three element sodium sulfur salts, which includes the step of supiilying the liquor to a calcining furnacc and evaporating the liquor to dryness and. calcining the dried product therein, the calcining being regulated to avoid smelting oi? the calcined product, leaching the calcined 1 roduct and incompletely causticizing the leached liquor.

141-. The method of treating residual liquor, resi'ilting from the cooking of wood with a liquor containing caustic soda and coon also coiitaining a three element compound of nliuni which contains sulfur, which coniirises concentrating the liquor, supplying tile concentrated liquor to a calcining furnace with completion of the evaporation and production of a. calcined product, regulating the calcining operation to give a calcined product containing a considerable amount of the three element sodium sulfur compound used in the cooking liquor, leachiug the calcined product and incon'ipletely caus 5ici71ing the same,

The method of treating residual liquor resulting-from the cooking of wooiil with a cooking liquor containing a preponderating mount of caustic soda and a lesser amount of a three element sodium sulfur compound ring tl: resulting solution to partially causticiszzed liquor containing icponderating amount of cau tic soda.

0 The method of treating re idual liquor, resulting from. cooking wood with a. cooking liquor containing caustic soda in a preionderating amount and also containing a three nentsodium sulfur compound which 'icn'iprises subjecting the liquor to concentration and calcination and regulating the calcining operation to avoid smelting ot the calcined product.

17. The method of treating residual liquor resulting from the cooking of wood with a cooking liquor containing a proponderating amount of caustic soda and a lesser amount ot a three element sodium sul-fur compound, which comprises subjecting the liquor to concentration and calcination, regulating the calcining operation to give a calcined product containing a considerable amount of the three element sodium sulfur compound, leaching the calcined product and incompletely causticizing the same to give a solution containing a prcponderating amount of caustic soda.

iii. The method of treating residual liquor, resulting from the cooking of wood .with a cooking liquor containing a 'ireiioudorating amount of caustic soda and also containing sodium suliite which comprises concentrating the liquor in multiple evaporators, feeding the concentrated liquor to a rotary calcining furnace and evaporating tho same to dryness and calcining the dried product therein, regulat-ing the calcination to give a calcined prod not containing a considerable amount oi sodium sullite, together with sodium carbonate and varying amounts of other sodium salts, leaching the calcined products and incompletely causticizing the same to give a solution containing a preponderatiug amount oi caustic soda.

19. The method oi regenerating a cooking liquor containing caustic soda and sodium sulfite from a residual liquor resulting from the cooking of wood with such a cooking liquor, wh1ch comprises concentrating the residual liquor, calcining the same in a rotary furnace with regulation of the calcination to avoid smelting, leaching the calcined material, incomplctcly causticizing a portion of the leacher solution, sulfiting another portion of the leached solution and mixing the cansticiZc-d and sullited portions.

20, 'ihe method of treating residual liquor resulting from the cooking oi wood with a cooking liquor containing sodium suliite which com pri "as calcining the residual liquor under conditions to substantially avoid oxidation or reduction of the sodium sullite.

21. The method of treating residual liquor resulti o troin the cooking of wood with a cooking liquor containing sodium sulritc which comprises calcining the residual liquor under conditions regulated to produce a calcined prmluct containing substantially only sodium sullilc and sodium carbonate.

22. 'lhc moi hod of treating residual liquor resulting :l'rom the cooking of wood with a cooking liquor containing sodium sulfite which comprises calcining the residual liquor under conditions regulated to substantially avoid the production of sodium sulfide and sodium sul late.

233. The method of treating residual liquor resulting iron! the cooking of wood with a cooking liquor containing sodium sullitc which comprises calcining the residual liquor, leaching the calci ed product and treating the leached liquor tor the production oi cookingliquor containing sodium sultite, the calcining and subsequent treatments being reg ulated to substantially prevent the formation of sodium thiosultatc in the cooking liquor.

In testimony whereoi' we atiix our signatures.

LINN BRADLEY. ED'WARD P. "VIoKEEFE. 

